.TH std::is_same 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::is_same \- std::is_same

.SH Synopsis
   Defined in header <type_traits>
   template< class T, class U >     \fI(since C++11)\fP
   struct is_same;

   If T and U name the same type (taking into account const/volatile qualifications),
   provides the member constant value equal to true. Otherwise value is false.

   Commutativity is satisfied, i.e. for any two types T and U, is_same<T, U>::value ==
   true if and only if is_same<U, T>::value == true.

   If the program adds specializations for std::is_same
   or std::is_same_v
   \fI(since C++17)\fP, the behavior is undefined.

.SH Member constants

   value    true if T and U are the same type, false otherwise
   \fB[static]\fP \fI(public static member constant)\fP

.SH Member functions

   operator bool converts the object to bool, returns value
                 \fI(public member function)\fP
   operator()    returns value
   \fI(C++14)\fP       \fI(public member function)\fP

.SH Member types

   Type       Definition
   value_type bool
   type       std::integral_constant<bool, value>

.SH Possible implementation

   template<class T, class U>
   struct is_same : std::false_type {};

   template<class T>
   struct is_same<T, T> : std::true_type {};

.SH Example


// Run this code

 #include <cstdint>
 #include <iostream>
 #include <type_traits>

 int main()
 {
     std::cout << std::boolalpha;

     // some implementation-defined facts

     // usually true if 'int' is 32 bit
     std::cout << std::is_same<int, std::int32_t>::value << ' '; // maybe true
     // possibly true if ILP64 data model is used
     std::cout << std::is_same<int, std::int64_t>::value << ' '; // maybe false

     // same tests as above, except using C++17's std::is_same_v<T, U> format
     std::cout << std::is_same_v<int, std::int32_t> << ' ';  // maybe true
     std::cout << std::is_same_v<int, std::int64_t> << '\\n'; // maybe false

     // compare the types of a couple variables
     long double num1 = 1.0;
     long double num2 = 2.0;
     static_assert( std::is_same_v<decltype(num1), decltype(num2)> == true );

     // 'float' is never an integral type
     static_assert( std::is_same<float, std::int32_t>::value == false );

     // 'int' is implicitly 'signed'
     static_assert( std::is_same_v<int, int> == true );
     static_assert( std::is_same_v<int, unsigned int> == false );
     static_assert( std::is_same_v<int, signed int> == true );

     // unlike other types, 'char' is neither 'unsigned' nor 'signed'
     static_assert( std::is_same_v<char, char> == true );
     static_assert( std::is_same_v<char, unsigned char> == false );
     static_assert( std::is_same_v<char, signed char> == false );

     // const-qualified type T is not same as non-const T
     static_assert( !std::is_same<const int, int>() );
 }

.SH Possible output:

 true false true false

.SH See also

   same_as                   specifies that a type is the same as another type
   (C++20)                   (concept)
   decltype specifier\fI(C++11)\fP obtains the type of an expression or an entity
